The key advantage of glyphosate (the active ingredient of Roundup) is that it is less toxic then table salt and it does not persist in the environment but breaks down to harmless chemicals very quickly. It is not surprising though that a hormone that is also a salt would mess up an animal that develops in fresh water (tadpoles). As for the Argentinian farmers... it includes many Monsanto chemicals that are banned in most countries but many were sprayed by USA helicopters to kill drug-making plants in their war on drugs efforts. Deformed children are just as expected as from using Agent Orange to kill trees in Vietnam and Cambodia.